Sorry to dampen you optimism, but these reactors are going to be totally useless after this. The reactor vessel will almost certainly be beyond repair and it is central to the entire plant. Economically it would be easier to just build a newer design of plant.

Sorry to dampen you optimism, but these reactors are going to be totally useless after this. The reactor vessel will almost certainly be beyond repair and it is central to the entire plant. Economically it would be easier to just build a newer design of plant.

They were planning to build two new reactors onsite, # 7 and #8. They'll probably end up with new ABWRs to replace the old clunkers. Note that a single ABWR outputs as much power as three BWR-3s or two BWR-4s so yanking three 40 year old dinosaurs does not necessarily mean they need to build three new ABWRs to take their place... My guess is they'll get one.

I'm hardly on their board of directors but most likely instead of adding 2 new ABWRs they'll probably simultaneously build the currently planned two, decon the old units 1 / 2 / 3 and build a nice new ABWR on top of the old site of 1 / 2 / 3.

Its is possible, that after this excitement, they'll yank all the old BWR-4s and the one decent BWR-5 and replace the whole works with ESBWRs. A pity GE gave up on the SBWR... That design would have been pretty much inherently safe in this situation. Of course I'm a little fuzzy on dates, I think the SBWR design was done a decade or two after the BWR-3 and BWR-4 were built at Fukushima and I don't remember why GE gave up on the SBWR design anyway (maybe the navy or other govt considered it too "sensitive", despite the navy's fondness for PWRs?)

Of course, it could be that, but it's far more likely he's trying to link the two (otherwise it's a completely inappropriate use of the semicolon). Bias in the news is not about lying, it's about creating emotional responses one way or another and getting people to link things together in a way that suits your agenda... in this case, an anti-nuclear one.

CNN.com are not the only ones, and there is even a link to an article insinuating American plants aren't safe (even though they come out and say it). This is persuasive writing... not necessarily factually incorrect, but not journalism, either.

Quite, that is some nasty reporting from someone who either has an agenda or who doesn't understand fuck-all. Also the rolling blackouts are due to the power plants having been shutdown. What do they expect? I have not heard about rationing, merely the president asking for people to conserve what they can. Lastly, most of the US does not suffer from earthquakes or tsunamis, so those similar reactors should be fine.

Someone is trying to blow this story sky-high. Why do they not focus on where the actual death

From my limited understanding of Japanese, the article refers to reactor #3, not explosion #3.I know Slashdot has limited editors, but shouldn't you at least click and check the links before posting such an important piece of news?

Many local news outlets will pick up and spread this piece of disinformation.

About 2 hours ago Tokyo Electric Co reported that they've decided to flood reactor #2 after its cooling died earlier during the day. It is not clear when and why it died. Anyway, since it died, flooding procedure was begun. However, they are so far failing to cover the whole active zone with water. TEPCO's official said that that is suggesting the reactor core has melted to some extent.

Just 10 minutes ago it was confirmed that water is flowing in slowly, and about half of the fuel is covered.

Indeed. It would help probably the global set of journalists to just refresh this page every hour or so [tepco.co.jp]. It was obvious for quite a while that an explosion outside the third reactor was likely, since it was experiencing exactly the same sequence as the first reactor.

The theory TEPCO is peddling is that the employee who was in charge of the pump that supplied water to the reactor allegedly left the pump while on inspection. During that time, the pump used up its fuel and stopped.

In the same sentence, the Minister of the economy, trade and industry said, that there is a serious chance of a partial meltdown of the active zone.

JUST NOW FROM THE TV (0:00 AM) : Currently, the water has again lowered and the core is again uncovered (and not cooling).

They've got limited staff who have been operating in crisis mode for days of likely working round the clock, are becoming ill from radiation poisoning, expect they may die, many have suffered personal losses recently, and half the country is in turmoil with tens of thousands missing or dead... I would think it's quite possible that some of them are not at their sharpest right now and may make mistakes. The human element is a real factor in plant operation, especially under extreme situations.

Not saying the guy isn't smart, but read the disclaimer at the top. He works for MIT, sure, but he's no nuclear physicist. In fact, it's basically stated that his "nuclear credentials" are based on his _father's_ expertise, NOT his. Essentially "my dad was a nuclear physicist so I'll write like I'm an expert too!". Again, he's smart and accomplished, but I'd submit he's sorely under qualified to make _any_ statements about the situation at hand.

The choice isn't between nuclear scientist vs random PhD, but between random PhD and sensationalist churnalism. The guy's writeup was a lot better than what I've read anywhere else over the past couple of days and his assertions seem to be supported by the small number of specialist sites that provide reasonable information.

Quite. Three lowsy hydrogen explosions, merely 2 of 6 reactors in partial meltdown at only 2 plants, hardly 200 irradiated and barely 200,000 evacuated... this is all bullshit, is it not? Slashdot has really turned into the Weekly World News of nerdy fear-mongering sensationalism. Thank God for the pro-nuke commenters that are setting the record straight. Nothing to see here.

And if all this had happened in the US and not some faraway country where it's all abstract? Still not news? Still all bullshit? You don't have to be "anti-nuke" to admit that yes, this is a serious crisis. I am heavily pro-nuke, but because it's not a religion or a cult to me, I don't close my eyes and blindly pretend this isn't actually, yes, a Pretty Bad Situation. I can admit that. Is it the end of the world, no, of course not, but sticking your fingers in your ears and going "la la la it's just a norma

I object to your assumption that credentials are more important than competence. He does not misrepresent his background, and his clear, simple, and dispassionate explanation justifies itself. It's not as if the facts are really in question.

To that I will not disagree, but there are Pro-Nuke shills and Anti's screaming on both sides, this one looks more aligned with the Pro side. The article basically states that nothing bad will happen and no radiation will leak. The gas that was vented has a half-life measured in mere seconds, blah blah blah. Meanwhile, US naval ships 100 miles off the coast are being moved due to detected radiation and people are being admitted to hospitals for exposure.

This article states "nothing to see here, move along" when it's obvious there _is_ something going on.

In short, this is just another fluff article written by a non-expert and people are gobbling it up like it's 100% fact. I mean look how it's being waved like a flag of truth and unbiased information when clearly it's already off the mark.

Note: I'm all for nuclear power and nuclear reactors. This situation is basically unprecedented and it's not surprising they are having serious problems. But I'd still take a nuclear reactor in my back yard over any of the fossil fuel plants _any_ day, anywhere.

"Dr Josef Oehmen studied Mechanical Engineering at the Technical University Munich and received a PhD, also in Mechanical Engineering, from the ETH Zurich. While working in industry, he obtained an MBA degree. He is currently employed as a Research Scientist at MIT. His major researchinterest lies in risk management along the engineering value chain and the application of lean principles to the product design process. J. Oehmen is a reviewer for several international j

Much like Three Mile Island (which also didn't release any significant radiation), this will set nuclear energy back years. And with the carbon problem and increasing dependence on fossil fuels, we need it now more than every. Solar and wind aren't ready, and so much progress has been made in nuclear plant safety.

From even the most optimistic sources I've read, solar costs something along the lines of 3-4 times more than nuclear per KwH. Wind power is supposedly cheaper than solar (by about about half), but can't deliver a consistent supply and is *heavily* dependent on location and weather (i.e., it's only cheaper if you're in a pretty consistently windy location with favorable weather). That's what I meant by "not ready."

First the Chernobyl clusterfuck turned nuclear power from The Answer To All Our Problems to A Scary Thing, then the non-event of TMI combined with some shitty old movie was enough to scare America off of it forever...now these events might be enough to damage nuclear power's reputation beyond repair with the rest of the international community. And what's left to take its place? All the fossil fuels you could ever want*, including lots of filthy, filthy coal.

The Chinese will probably push forward with their nuclear plans. On one hand, it's good that it will reduce the coal use of one of the planet's biggest energy consumers, on the other hand, China has a reputation for not giving a fuck about the environment or safety (they're in the middle of their Gilded Age after all), and the last thing anybody needs is another Chernobyl, plus any improperly set up Chinese nuclear waste sites won't get a super-funded cleanup any time in the forseeable future. Maybe they'd get some political prisoners to do the cleanup work to save costs on hazmat suits and decontamination gear.

First the Chernobyl clusterfuck turned nuclear power from The Answer To All Our Problems to A Scary Thing, then the non-event of TMI combined with some shitty old movie was enough to scare America off of it forever

A while back I was watching World's Toughest Fixes and they would not show the cooling buildings at the nuke plant where the show was filmed. I guess that now makes sense (one can argue it is theater). Why blow up the reactor proper when you can go after a much softer target and achieve basically the same effect. I am all for nuclear power but this needs to be addressed IMHO.

Because it might have been cheaper to cut some corners with existing equipment than build a new reactor every time some scientist comes along with the next great thing? It might have been more profitable to do things the way they have been done, and when the sh*t hits the fan the nuclear industry can still count on their (highly moderated) forum posters to deny any problem.

This may also be a reason why some folks here don't trust the nuclear industry too much...

All of those people who died were killed by the tsunami or the quake.
Okay, technically, there have been a VERY SMALL (like on the order of a few dozen) number of injuries and a few fatalities directly related to the reactors. But those were all among people who were actually *working in* the power plants.

And that is the main reason why all that is interesting. Those reactors are quite old and unsafe (by today standards), they were hit by one of the biggest quakes ever measured, and submerged after that. Yet, just a few died from an hydrogen explosion, and the radiation level looks quite workeable. It seems that safe reactors should be quite safe indeed.

Ok, but I'm still waiting for the truthfull assessment of the situation after everybody calms down.

I live in Japan and have been following this news all day. The info in the headline and summary about the the reactors is complete incorrect. As to what has actually been happening:

First, the linked article is from 7 hours ago and is referring to the second explosion at Fukushima Daiichi of Reactor #3. The current situation as of 8PM Japan time was that the cooling system of Reactor #2 finally died and they just recently started filling it with seawater like the other reactors. This reactor is likely to cause another hydrogen explosion like the other two failed reactors before it. Also like the other reactors, this one may have suffered from some partial melting of its fuel rods.

Secondly, the article implies that thousands have died as a result of the problems at the Fukushima reactors. THIS IS NOT THE CASE! There have been reports of non-serious injuries and VERY mild radiation contamination but nothing that warrants any kind of panic yet.

Slashdot editors, please rewrite or delete this article, it is just spreading misinformation!

So, let's see. So far these plants have endured an earthquake 10 times what they were designed for (8.9 Richter earthquake. Design was for 7.9. Modulo distance/ground transmission from epicenter.), a 23 foot tsunami that took out backup generators and the switchyard taking out all but battery power, failures of the RCIC backup cooling system, and 2 massive hydrogen explosions that took out the buildings around the containments.

And thus far no significant release of radioactivity.

And we've got people saying the plants are fragile and unsafe?

What do you want? The North Koreans hitting it with bunker busters? A meteor strike?

So, let's see. So far these plants have endured an earthquake 10 times what they were designed for (8.9 Richter earthquake. Design was for 7.9. Modulo distance/ground transmission from epicenter.), a 23 foot tsunami that took out backup generators and the switchyard taking out all but battery power, failures of the RCIC backup cooling system, and 2 massive hydrogen explosions that took out the buildings around the containments.

One thing you can take from that is, whatever scale of disaster you plan for, nature (or potentially mankind) can go one better. Build your nuclear plants to withstand a 7.9 and along comes an 8.9 accompanied by massive flooding. Build a bomb proof pair of skyscrapers, and lo, someone flies passenger airliners into them. I can't predict any better than you what the next surprise will be.

The largest earthquake ever recorded was 9.5 in 1960 in Chile. The Japan quake was only the 5th largest. Any nuke plant built after 1960 should have been designed to withstand at least a 9.5, especially in a place like Japan. Designing for 7.9 is accepting an inevitable disaster.

So far these plants have endured an earthquake 10 times what they were designed for (8.9 Richter earthquake. Design was for 7.9. Modulo distance/ground transmission from epicenter.),

The richter is base-10 logarithmic, but it is measuring amplitude. However, the destructive power of an earthquake is related to the energy released more than the amplitude, and the energy released is a function of the 3/2 power of the amplitude.

Hence a 1 point increase is actually 10^3/2 or about 32 times as powerful.

The coast of Japan is smashed, tens of thousands are missing with many of them dead, and you're more concerned about a potential radiological release?

Get a sense of proportion.

It seems reasonable to say that a lot of those deaths, injuries and property damage were unavoidable though. It's simply not practical -- possible even -- to convince people not to build homes, roads or workplaces on low coastal land, especially if that includes 10 miles inland.

However, it seems fairly practical to avoid building things with potentially hugely dangerous failure modes, when there are alternatives. In know the alternatives seem unpalatable to some people, but the sour flavour of this alternat

Truly, we either need to evolve civilisation so that this is less true. Yes, there are renewable sources to explore, but at the same time, we should be looking at ways to reduce our energy needs. It's compatible with our basic desire to save money anyway.

As for stable power bases -- I don't know why there aren't more hydroelectric schemes (not generating power from a river-filled reservoir, but pumping water uphill when the sun's out or the wind turbines are spinning, and running it downhill through turbine

The future of nuclear power, if there is any, is something like a pebble bed reactor, which is passively safe: all of the support equipment, all of the nuclear plant personnel: it can all fail and they can all leave, and nothing bad will happen:

The DESIGN PHILOSOPHY of 1960s era nuclear power is what is killing nuclear power as a viable alternative in this world. Yes, people react in fear and panic and hysteria. So? Did you honestly expect any other reaction possible amongst the general populace, ever? Panic and hysteria is a CONSTANT of humanity. Their impression of nuclear power has been, uh, contaminated, and that's just simple human psychology, there's no getting around that.

So I blame one group here: 1960s, 1950s era nuclear engineers. It is their fault why nuclear power is becoming politically unacceptable. They designed plants that needed to be actively safe. THAT is the real reason we are having problems in Japan now, why we had problems at 3 mile island, why we had problems at Chernobyl: someone has to be there, certain equipment has to work, or there will be trouble. BAD DESIGN. It's just a matter of time before operator error or a geological/ meteorological event causes the active safety system to fail. Nuclear engineers of the '50s and '60s honestly should have foreseen that. Nuclear plants, from the beginning, should have been designed that should something bad happen, the system just naturally gravitates to a harmless state. But in the 1960s, they put in plants that naturally gravitate to a harmful state, and require constant effort to keep safe. Really, really bad design.

Nuclear engineers from a half century ago genuinely failed us. They genuinely fucked up, and we are paying for their shoddy design. And so is the future of nuclear power. Because we have passively safe nuclear designs like pebble bed reactors now. But we may never see them in full use, ever, because public opinion has been poisoned, maybe irreparably. You can't blame the common man for that. He cannot shrug and forget being irradiated. But nuclear engineers, they should have known, they should designed better systems. It is their fault.

Third generation plants (the kind who's design is currently being held up in congress by idiocrats) use a passive emergency cooling system that circulates cooling water using natural convection, and it does not require electric pumps to function.

This might have been said in one of the many other replies to this comment, but the German pebble bed reactor was one massive fuck-up. The pebbles did not move as planned, temperatures were way higher than thought (and this was only discovered about 10 years _after_ shutting it down), and there were cracks in the foundations where pebbles got stuck due to this, all of this without being noticed. Also, some radiating leaked due to this. So inherently safe is not necessarily true, one can still screw thinks u

Don't blame the engineers. We were just figuring out what constituted a good plant design at that time. Considering the lack of experience, it seems they've done a damned good job of it too. For all of the fearmongering headlines, no plant of this design has ever lost containment or even suffered a complete meltdown (which, contrary to the brightest engineers in hollywood, does not lead to loss of containment, much less a ball of nuclear waste destroying the earth's core and such).

as an aside, both CANDU and pebble beds still have potential problems and weaknesses. nuclear power is inherently dangerous. so what i call upon the nuclear engineers of the world is to improve on CANDU and pebble bed designs: make nuclear reactor design as passively safe as possible.wWe can't afford for you not to. we can't afford radiation leaks and melt downs. As a simple matter of not polluting the world and

The real fallout that Japan needs to worry about is that they have permanently lost a substantial part of their capacity to generate electricity and won't be able to replace it anytime soon. The US and other countries with these high power nuclear plants should learn a lesson. It is better to build several smaller plants instead of a few megaplants. That way, if one of them is out of commission, it is not a total loss to the power grid.

The lack of power in Japan will be a significant issue as the country tries to react to the quake and tsunami and will hamper long term recovery efforts, too.

He doesn't. Reading the summary it is very clear that the amount of radiation that will be leaked is proportional to the number of deads caused by the Tsunami.
But don't ask me how, I'm no nuclear scientist.

That writeup was a godsend. So, if they've flooded the uncooled reactors with boric-acid and seawater nothing could possibly go wrong - and if they had been unmanned and allowed to meltdown, nothing would have gone wrong either. And the materials released in the radioactive steam decay completely within seconds.

There's some interesting information buried inside that article too: they keep spent fuel rods in a pool in a nearby building or somesuch, that (if uncooled) will also melt. I saw pictures of such a storage once; it looked as if the fuel was gripped by industrial robot cranes and pulled into a "submerged" underground pool through a tunnel.

This Josef dude is one of the overly confident/underly prudent types. As an example that Josef suffers from this dangerous deficit, he put his name to a document saying nothing bad will happen. Since then, reactors 1-3 have been exposed to explosions, a spent fuel pool is probably exposed to the air, and reactor 4 building is reportedly on fire. The news is no longer talking about micro-sieverts, it's now milli-sieverts. The evacuation zone has been expanded to 30 km, and NHK is describing what to and w

So many people think of "nuclear meltdown" as "nuclear explosion". Not the case. Meltdown is just that; Melting down of the fuel. Gravity dictates that this fluid fuel will go down, so meltdown is of very little concern to anyone except the reactor ops. Remember that reactor 5 at Chernobyl exploded because of their idiocy on several levels, not because of any fault with the plant (which would have functioned perfectly well if the operators had followed procedure correctly and vented the pressure vessel when required).

I say bravo to the Japanese. They've done very well throughout all of this. The deaths reported are a result of a 9.0 earthquake and linked tidal wave, not any nuclear incident, and that just goes to show how safe it is. Interesting factoid from the article; The reactors were designed to withstand an 8.3 Richter scale quake. As the Richter scale is logarithmic, they withstood a quake seven times their maximum. The only "Woops!" point was when they shipped in portable generators to replace the tsunami-swamped diesel backups... With the wrong plugs.

It doesn't matter. Humanity will overreact as usual, and any failures of these old reactors will completely kill *any* public discussion of new nuclear tech for decades to come. Better hope there's some massive breakthrough in solar or wind or something else, because one door to energy independence was just slammed shut this week.

Nothing detectable on a whole ocean (I think). Even if the rods pack a big punch, you have around 1,260 billion billion Litre(or Kg if we assume it's pure water, even though it isn't) of water in the oceans. So you need around 5 million billion billion Joule to raise the oceans temperature by 1 degree Celsius. That's several orders of magnitude of the reactors ability.

Should the meltdown reach the sea, I probably won't be eating the local sushi for a while, some of those radioisotopes are either chemically nasty or fairly peppy alpha emitters.

Thermally, though, almost totally irrelevant. The three reactors that are running into trouble are a 460MWe and two 760MWe units. In rough numbers, I think that such plants might manage efficiency in the ~25% range, which would correspond to total heat outputs of 1840MW and two at 3040MW(under optimal, full-power operating conditions).
1 calorie is the energy required to raise the temperature of 1gm of water by 1 degree celsius, 4.184 joules. If we go with our(pessimistic) assumption that the meltdown mass is putting out heat equivalent to the reactor operating as designed, that means 1840 million J/s or roughly 440,000,000 calories/s. That would mean that, per second, at maximum output, the core would be good for raising the temperature of 440,000L of water by 1 degree every second.

More plausibly(because there is no way that a meltdown blob is going to come in contact with that much water that fast), it will superheat the water immediately surrounding it, generating some very, very toasty steam(some of which will lose energy to the surrounding water, heating it, some of which will escape into the atmosphere). Thus, a fair percentage of the thermal energy will into the atmosphere, or into overcoming the enthalpy of vaporization of water, which is fairly high.

Even if 100% of the thermal energy from all three crippled reactors went directly into heating water (7920MW or ~1.9 billion calories/s) it would be facing the ~1.34442 x 10^21 L of water in earth's oceans. That would provide ~1.4x 10^-12 calories/s for each Liter. If we make the (highly pessimistic) assumption that the reactor meltdown blobs would continue at full power for a decade(315 569 260 seconds), that would correspond to a 0.000445977891 degree (celsius) rise in world ocean temps.

Spilling the fun stuff that you find in a live reactor is a terrible plan. Wholly ill advised. Don't do it. Not really a thermal concern, thon,

(theorizing, former nuclear control room operator here from a plant of the same style, GE Boiling Water Reactor, as the ones with the problem)

They've at a minimum lost coolant to relief valve operation after they lost cooling due to loss of offsite (and local emergency diesel) power. They possibly also have some pipe breaks within the drywell containment structure. The relief valve operation is a form of "zero power" cooling unto itself, but you need to make up for the lost coolant somehow.

Nearly all emergency procedures that have a chance of keeping the plant intact depend on power being available, without power, you have to resort to destructive methods (sea water pumped in via fire pumps for instance) to keep things cooled off. Note also, that the equipment that would normally reduce or eliminate hydrogen buildup (the apparent cause of the building explosions) also require power.

While the earthquake was the root cause, the seawater being able to reach and apparently shutdown the emergency diesel generators onsite is why the problems got MUCH larger than what could have been.

As far as I understood, the seawater+boric acid solution has been applied to reactors that were scheduled to be scrapped quite soon anyway. For an operational reactor, you do not want to do this until the very last moment. As for why there are no other power sources available to power the pumps... that is a good question.

Yeah, a total overreaction, only 2 nuclear power plants are failing, of 6 reactors, only 2 are in partial meltdown; less than 200 people were irradiated, less than 200,000 were evacuated. Why is this even news? Sensational journalism makes me nauseous.

If people were sane and less reactionary, this is actually quite the demonstration of how incredibly resilient it all was.

First off, humans being sane and non reactionary is hardly the default setting. Secondly, if you look at the before and after satellite pictures of the plant, it's apparent that structurally the system performed quite well. However, the little details like generator siting and aspects of defense in depth, not so much. So they may have nine out of ten things right, even with bonus points for being able to do this on such an old reactor system, but they seem uncomfortably close to losing local containment

It's funny, because last week the republicans were talking up nuclear power, too... and now the media (what I heard this morning, anyway) is firmly planted in trying to show why republicans are idiots for pushing nuclear power when it was part of Obama's agenda, too.

Ahh, to politics and never letting a crisis go to waste, and to never letting facts about Three Mile Island and the current tragedy get in the way of a good story.

What would have happened if they had wind power? Would the towers sustain under 9.0+ earthquake? Support the rushing waters? What about solar? Would the panels/mirrors hold against a wave of crushing water?

I'm not quite sure what sustainable power you are suggesting and what better outcome you are alluding to.

I think the opposite. If Japan manages to get through this with only minor radiation problems (as so far) I think it will be a positive for nuclear energy. I mean, WTF more could you possibly do? A Mag 10 quake right under the reactor core? One thing that will come out of this is that both Japan and the US currently require backup power for the cooling system of only about 12 hours while the Eurolanders require 24-48 hours. There will definitely be a push to try to up this to 72 hours though of course practicalities may get in the way.

If a fuel assembly were to overheat and deform within its fuel channel, the resulting change of geometry permits high heat transfer to the cool moderator, thus preventing the breach of the fuel channel, and the possibility of a meltdown. Furthermore, because of the use of natural uranium as fuel, this reactor cannot sustain a chain reaction if its original fuel channel geometry is altered in any significant manner.

Yes, they could just drain off all the water completely (so no more steam generation and no risk of pressure build up) but it would totally wreck the core since it would melt into its concrete containment system, then you'd have a big, broken mess left over (although with all the radiation contained) that you'd have to clean up.

This way they are hoping the core is not totally wrecked (although it will definitely be damaged and require extensive repairs before being used again, if ever), so that it is easier to clean up and reprocess the fuel, with the problem that because you are pumping water in there (at less than required flow rate) it's boiling off quickly raising the pressure very high and cracking to H2 and O2, which just love to react very exothermically - causing those explosions we have seen when they vent this pressure out into the atmosphere.

The best case is that they keep doing what they're doing, and try to minimise the chance of H2 explosions, so that it will be easy to dismantle the core when it is cold. If they just let it melt there will be no more hydrogen explosions, but they'll have a molten mess of fuel and reactor parts spread out inside the concrete containment shield that will be considerably more annoying to clean up (but still completely safe from an external observer point of view - it;s designed to fail this way in the event of a full meltdown).

I think the problem is that everyone is equating "meltdown" to mean "will explode like Chernobyl", which is not what happened there - the Chernobyl explosion was a catastrophic steam explosion like a pressure cooker exploding. The core didn't melt down until after the explosion happened.

These "little" explosions we are seeing in Japan are because they are releasing the pressure in a controlled manner - if they just left it (and disabled the safety systems) then it could face a similar problem to Chernobyl, with the reactor being destroyed by a steam explosion, with the crucial difference that the core of this reactor is totally shielded (Chernobyl's RBMK reactors were too big to contain without it costing a ridiculous amount, so the building was the secondary containment structure - and it fell apart like tissue paper, as expected).

It's also slightly different in Japan - the reactor is "off" so the uranium fission reaction has stopped, and it's just residual heat and decay product heat to be dealt with, so it's a relatively slow and controllable heating. In Reactor 4 in Chernobyl, the fission reaction was very definitely running - but was poisoned due to neutron absorbing products (the core was running at much too low power), and when these were gone, and with the rods all the way out, the reactor spiked to a massive level which flashed all the water in there to steam almost instantly, which blew the lid off the top - just like throwing an aerosol can onto a fire, or shooting it with an air rifle. They had no time to relieve the pressure.

Chernobyl's RBMK reactors were too big to contain without it costing a ridiculous amount, so the building was the secondary containment structure - and it fell apart like tissue paper, as expected

IIRC it's not that the RBMK reactors themselves were too big, but that they were designed to have their fuel replaced whilst the reactor was running and keeping all the loading gear inside containment was space prohibitive. There's an awesome cutaway model here http://neutron.kth.se/gallery/power_reactors/Ignalina_model.JPG [neutron.kth.se] that shows the colossal crane/gantry above the core, along with what basically amounts to a shed roof covering the reactor core. Not pictured is the cooling pond, which sits parallel to the core (and takes up more space) that the spent fuel rods are dropped into.

Fitting all that folderol inside decent containment would be very expensive, because you now need at least twice the height and width of the reactor to fit everything in. So why bother? Allowing refuelling whilst the reactor is running meant a) you wouldn't need to close the reactor down to refuel it and b) you could make lots of weapons-grade plutonium very quickly. Weapons grade stuff requires very short fuel runs on a low burnup (exactly what you don't want in a reactor for power generation), whereas extracting P239 from all the other plutonium isotopes in "regular" nuclear wastes is exceptionally difficult. Since these reactors are expensive, lots of countries decided to cheap out and build dual purposed reactors which, after enough warheads had been made, could then be converted to civilian fuel loads. Hence you had a bunch of suboptimal design decisions taking place, such as the lack of containment on RBMK and other reactors. Yay for the cold war.

Not meant as a nitpick BTW, just thought people might find it interesting.

Those reactors are already destroyed. They will never be operational gain (it says that in the article I linked to).

Careful, reactors 1 / 2 / 3 were online hot and currently self destructing due to decay heat. On the other hand, 4 / 5 / 6 were off for maintenance and as far as I know are cold shutdown. They will be restarted in the future assuming they didn't take too much tsunami damage and/or explosion damage from 1/2/3 popping. You will not be too surprised to learn that 1 / 2 / 3 are the oldest reactors, some 40 year old clunkers. The newer design 4 and 5 are not too bad and 6 is actually pretty decent. And they're planning on building some new ABWRs 7 and 8 onsite. One new ABWR generates almost as much power as 1, 2, and 3 put together.

So the idea is to minimize contamination and damage to reactors 4 / 5 / 6. Remember only one of Chernobyls reactors melted down, the other continued generating power for a decade or something like that.

Those reactors are already destroyed. They will never be operational gain (it says that in the article I linked to).A complete meltdown will lead to a huge discharge of radioactive waste similiar to Chernobyl. That's what they are trying to avoid at all costs. The fact that the reactor is "off" is irrelevant.

No it won't - if these cores completely melt down they will be safely contained within the enclosing concrete containment (which is inside the building), and completely encloses the reactor.

If they melt down there will just be a puddle of fuel and melted reactor in the bottom of this structure, which is designed like a dish to spread it out thinly so it cools quickly, but it will all still be totally sealed inside.

There is no way it will be spread over hundreds of miles (or even just outside the plant itsel

Not so, not even close. BWR model 3 (example is unit 1 at this site) had a mark1 concrete containment system and BWR model 4 (examples are units 2 and 3 at this site) could have been built with mark1 or mark2 containment systems.

A gross simplification is mark1 is a big concrete building with a little concrete building inside it and a steel shield inside that little building. In all the pics you can see the big building popped pretty much as designed and the little building inside it is still claimed to be

The core is already subcritical, adding boric acid just acts as a neutron sponge to capture thermalised neutrons (that are being moderated by the water they're pumping in). The source of these neutrons is the short lives radionuclides that form as part of the normal operating reaction, ie, not the uranium.

With adequate cooling you don;t have to worry about them - there aren't all that many, relative to the normal running of the reactor and normal cooling is enough to deal with the heat produced as these pro

Hey all - I think this is a false alarm. If you translate the original article, this is what you get... (albeit a painful translation...)

It is hydrogen explosion indoor shunting appeal with unit No. the first Fukushima nuclear power generation 3

A big explosion got up with unit No. 3 of the first Fukushima Nuclear Power Plant of Tokyo Electric damaged by East Japan great earthquake disaster (Fukushima Okuma-cho) at about 11:00 a.m. on 14th. According to Ministry of Economy, Trade and Industry Nuclear a

Yeah, the way I read this is that there was an explosion at the third unit, meaning unit number three, not a third explosion. Honestly I'm not too concerned about this, it seems like they are pumping water to keep the cores cool, and will likely achieve cold shutdown. The news media is making hay with this for ratings, but really, it seems like things are progressing well, all things considered. Not that things couldn't go wrong, but I think not.

The problem is, what to replace it with? Coal has an even higher death and pollution rate, the worlds running out of natgas so forget that. That leaves, uh, going all "Pol Pot" on the population, I guess?

If we assume the market-driven-economists got it right, we should ensure that investors in nuclear power (and all the others) are held liable for the long term cleanup costs, and any emergency costs associated with their activities. The cost will rise; the cost of coal/oil/gas will rise. Alternatives will arise from the innovation of entrepreneurs.